I'm pretty sure I've had this rosy barb for about five years now and throughout the last year at least I have noticed that it is quite fat. With its red coloration I assume it is a male and therefore not pregnant, and due to the length of its survival not seriously diseased either. I have noticed that my other rosy barbs are generally fat as well but none to the same degree.

Is it normal for rosy barbs to as fat as mine are? Does it increase with age, and if so, why does the one I've had for about three years look so much healthier than any of the others? I bought three around November and the seem to be somewhat fat as well.

They do not seem to be overeating, if anything they act as if they are starved. Recently I have seen the old fat one swimming downward through the bubble stream which looked odd and just today I found it lying upside down, wedged in a plant. I was sure it was dying, it didn't even react when I tapped it with the net. Then, within minutes it was swimming around again. Apparently it was sleeping! I've never heard of a fish sleeping upside down before, well maybe the upside down catfish but anyway I'm fairly sure thats not normal.

Could it be overfeeding, if so, why do all the fish in the tank act starved, even the black mollies, and pearl gourami? Could it be the diet? Or that I add a small amount of salt to every water change? Or a long term infectious disease transferable only to rosy barbs? Or perhaps this is normal. Hopefully you can help. Here are some pictures of my rosy barbs.
Five year old rosyUpside down in plantThree year old rosyNew rosy's

All your fish look fat but that one male has a tumour or other growth.

Please stop adding salt as you have no way of measuring the concentration in the tank and the mollies will be fine but it won't be helping the other fish.

Try adding some veggies for the barbs and mollies. They are good algae eaters and will do better with a vegetable component to their diet.
I would add a bunch of Egeria but you could add a leaf of romaine lettuce or similar and only feed dry food five days a week.
The gourami is a bug eater so an occasional feed of defrosted larvae -bloodworm etc. would be a good idea and a treat for the others.
Fish in the wild spend much of their time eating but in a tank eat the equivalent of as much Macdonalds as they can stuff in their mouths a couple of times a day.

Thank you for the help. It passed away today, it is so sad that a fish that has been with me for so long has died. I will stop adding aquarium salt and I will start with the diet of flakes and freeze dried bloodworms and medley only five days a week. I will also be starting out boiled romaine lettuce and perhaps zuccini.